[YouTube] Add ability to generate manifests of progressive, OTF and post live streams

A new class has been added to do so: YoutubeDashManifestCreator.
It relies on a new class: ManifestCreatorCache, to cache the content, which relies on a new pair class named Pair.
Results are cached and there is a cache per delivery type, on which cache limit, clear factor, clearing and resetting can be applied to each cache and to all caches.
Look at code changes for more details.

Author: AudricV